icon does not appear on desktop when using outside connections

Every time I try to load pictures from a camera, use a Maxtor One Touch 4 to load programs, the icon does not appear on my desktop. I first thought this might be a port problem. I tried connecting other devices to the other ports like the printer, and it worked fine. It seems anytime I use an outside device connected to my Mac Mini, the computer does not recognize it. This seemed to have started when I connected a new printer